Pollution Control and Resource Recovery: Sewage Sludge

By Zhao Youcai and Zhen Guangyin

Pollution Control and Resource Recovery: Sewage Sludge discusses several traditional and new environmentally friendly technologies for sewage sludge treatment and disposal. In addition, the book covers a range of new initiatives that are underway to promote and accelerate the development of related sciences and techniques.

The book's authors builds a framework for developing various sustainable technologies for sewage sludge treatment and disposal, including advanced dewatering through chemical conditioning, solidification/stabilization, reuse for the development of construction and building materials, anaerobic bioenergy recovery, sanitary landfill, and odor control.

• Explains environmentally friendly technologies for sewage sludge treatment and disposal, including advanced dewatering through chemical conditioning, solidification/stabilization, and anaerobic bioenergy recovery
• Includes valuable guidelines for engineers to address sludge issues, such as sanitary landfill and odor control
• Presents new developments and techniques that are on the horizon

• Language: English
• Publisher: Elsevier Science
• Release date: Oct 27, 2016
• ISBN: 9780128118542

Zhao Youcai

Zhao Youcai, is currently a professor of environmental engineering at School of Environmental Science and Engineering, Tongji University. He got bachelor degree from Sichuan University (1984) and Ph.D. from Institute of Chemical Metallurgy (now Institute of Process Engineering), Chinese Academy of Sciences, Beijing (1989). After finished Post-doctoral research work at Fudan University, Shanghai, he joined in Tongji University in 1991. Meanwhile, he had ever worked at Aristotle University, Greece, National University of Singapore, Tulane University, USA, and Paul Scherrer Institute, Switzerland, for 4 years as research fellow or visiting professor. He had authored or co-authored 200 publications published in peer-reviewed internationally recognized journals, 480 publications in China journals, authored 9 English books (at Elsevier and Springer) and authored or co-authored 98 Chinese books (as an author or Editor-in-chief), 4 textbooks for undergraduate, graduate and PhD students with a fourth edition of undergraduate textbook (in Chinese). Currently, his research interests include treatment and recycling of municipal and rural solid waste, construction and demolition waste, hazardous waste, industrial waste, electric and electronic waste, and sewage sludge, and polluted soil.

Book preview

Pollution Control and Resource Recovery

Sewage Sludge

Zhen Guangyin

Zhao Youcai∗

∗State Key Laboratory of Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Tongji University, Shanghai, China

Table of Contents

Cover image

Title page

Copyright

List of Contributors

About the Authors

Preface

Summary

Abbreviations

Chapter One. Sewage Sludge Generation and Characteristics

1.1. Sewage Sludge Production

1.2. Special Features of Sewage Sludge

1.3. General Processes of Pollution Control and Resource Recovery for Sewage Sludge

1.4. Sanitary Landfill of Sludge

Chapter Two. Enhanced Sewage Sludge Dewaterability by Chemical Conditioning

2.1. Enhanced Dewatering Characteristics With Fenton Pretreatment

2.2. Enhanced Dewaterability Using Fe(II)-Activated Persulfate Oxidation

2.3. Novel Insights Into Enhanced Dewaterability by Fe(II)-Activated Persulfate Oxidation

2.4. Synergetic Pretreatment by Fe(II)-Activated Persulfate Oxidation Under Mild Temperature

2.5. Combination of Electrolysis and Fe(II)-Activated Persulfate Oxidation for Dewaterability

2.6. Hydrothermal Pretreatment of Dewatered Sludge for Dewaterability

2.7. Filtration Improvement of Zinc Sludge by Using Unconventional Alkalization Sequence

2.8. Enhanced Dewatering of Waste-Activated Sludge by Composite Hydrolysis Enzymes

2.9. Practical Significance for Mechanical Dewatering Processes

Chapter Three. Sewage Sludge Solidification/Stabilization and Drying/Incineration Process

3.1. Effect of Calcined Aluminum Salts on the Advanced Dewatering and Solidification/Stabilization

3.2. Aluminate 12CaO·7Al2O3-Assisted Portland Cement-Based Solidification/Stabilization

3.3. Hybrid Cement-Assisted Dewatering and Solidification/Stabilization of Sewage Sludge with High Organic Content

3.4. Stabilization/Solidification Using Magnesium Oxychlorides Cement

3.5. Vaporization and Depression Control of Heavy Metals in Sludge Subject to Incineration

3.6. Production of Sludge Solidifiers and Their Commercial Applications

Chapter Four. Making of Sewage Sludge-Derived Controlled Low-Strength Materials (CLSMs)

4.1. Performance Appraisal of Controlled Low-Strength Material Using Dewatered Sludge and Municipal Solid-Waste Incineration Bottom Ash (MSWI BA)

4.2. Mechanical and Microstructural Perspectives of Controlled Low-Strength Material Cured for 1Year

Chapter Five. Harvest of Bioenergy From Sewage Sludge by Anaerobic Digestion

5.1. Overview on Current Advances in Sludge Pretreatment to Improve Anaerobic Biodegradability

5.2. Anaerobic Digestion Technique and Combined ElectricalAlkali Pretreatment to Increase the Anaerobic Hydrolysis Rate of Sludge

5.3. Influence of Zero-Valent Scrap Iron (ZVSI) Supply on Methane Production

5.4. Mesophilic Anaerobic Codigestion of Waste-Activated Sludge (WAS) and Egeria densa: Performance Assessment and Kinetic Analysis

5.5. Application of Aged Refuse to Boost Bio-Hydrogen Production From Food Waste and Sewage Sludge

5.6. Toxic Effect of Antibiotic Cefalexin on Methane Production From Sewage Sludge

Chapter Six. Pollution Control and Recycling of Sludge in Sanitary Landfill

6.1. Design and Construction of a Sludge Landfill

6.2. Sanitary Landfill of Dewatered Sludge and Characterization of Stabilization Process by Particle Size Distribution and Humic Substances Content as Well as FT-IR

6.3. Combination of Combustion With Pyrolysis for the Stabilization Process of Sludge in Landfill

6.4. Variation of PAHs’, PCBs’, and OCPs’ Contents and Influencing Factors in Sludge Landfill Process

6.5. Abiotic Association of Phthalic Acid Esters With Humic Acid in a Sludge Landfill

6.6. Chemical Reduction of Odor for Sludge in the Presence of Ferric Hydroxide

6.7. Stabilization of Sewage Sludge Using Nanoscale Zero-Valent Iron (nZVI) for an Abatement of Odor and Improvement of Biogas Production

6.8. Use of Core–shell Zero-Valent Iron Nanoparticles for Removal of Sulfide in Long-Term Sludge Anaerobic Digestion

6.9. Treatment of Aged-Landfill-Leachate Using Aged-Sludge-Based Bioreactor

6.10. Landfilling and Stabilization Process in General for Sludge Sanitary Landfill

References

Index

Copyright

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List of Contributors

Zhen Guangyin

Tongji University, Shanghai, China

Tohoku University, Sendai, Miyagi, Japan

Zhou Haiyan,     Shanghai Laogang Waste Disposal Company, Shanghai, China

Chen Haoquan,     Shanghai Environmental Engineering Company, Shanghai, China

Zhang Hua,     Tongji University, Shanghai, China

Ma Jianli,     Tongji University, Shanghai, China

Tai Jun,     Shanghai Design Institute of Environmental Sanitation Engineering, Shanghai, China

Su Lianghu,     Tongji University, Shanghai, China

Zhang Meilan,     Shanghai Laogang Waste Disposal Company, Shanghai, China

Tang Ping,     Tongji University, Shanghai, China

Huang Renhua,     Shanghai Laogang Waste Disposal Company, Shanghai, China

Chen Shanping,     Shanghai Design Institute of Environmental Sanitation Engineering, Shanghai, China

Chai Xiaoli,     Tongji University, Shanghai, China

Lu Xueqin,     Tohoku University, Sendai, Miyagi, Japan

Zhu Ying,     Tongji University, Shanghai, China

Zhao Youcai,     Tongji University, Shanghai, China

About the Authors

Zhen Guangyin is currently JSPS research fellow at the National Institute for Environmental Studies (NIES), Japan. He received his BE degree in Environmental Engineering from Hunan University, China in 2008 and his PhD from Tongji University, China in 2014. Prior to joining in the NIES, he worked as a visiting researcher at the Tohoku University, Japan. He has authored or coauthored 30 peer-reviewed international papers, 5 Chinese papers, and 4 invited book chapters. His principal research interests lie in sewage sludge treatment and renewable energy conversion (anaerobic digestion, microbial electrolysis cell, etc.).

Zhao Youcai is currently a professor of environmental engineering at School of Environmental Science and Engineering, Tongji University. He got bachelor degree from Sichuan University (1984) and PhD from Institute of Chemical Metallurgy (now Institute of Process Engineering), Chinese Academy of Sciences, Beijing (1989). After finishing his postdoctoral research work at Fudan University, Shanghai, he joined in Tongji University in 1991. Meanwhile, he had also worked at Aristotle University, Greece of Thessaloniki, National University of Singapore, Tulane University, United States, and Paul Scherrer Institute, Switzerland, for 4  years as research fellow or visiting professor. He had authored or coauthored 138 publications published in the peer-reviewed internationally recognized journals, 420 publications in China journals, and authored or coauthored 75 books (as an author or Editor-in-chief). Currently, his research interests include treatment of municipal solid wastes, sewage sludge, hazardous wastes, polluted construction wastes, and industrial wastes.

Preface

The increase in wastewater treatment activities has been confronted with a dramatically increased amount of sewage sludge, which accounts for up to 50–60% of the total operational costs of a wastewater treatment plant. Sewage sludge floc is a multiphase medium and constitutes the vast majority of components that hamper its dewatering and subsequent disposal or reuse. The treatment and disposal of sludge represents a bottleneck in water industries, which has caused an urgent call for the development of cost-efficient approaches to reduce and minimize sludge production.

During the last decennia, the authors have conducted a series of scientific research on developing various sustainable technologies for sewage sludge treatment and disposal, including advanced dewatering through chemical conditioning, solidification/stabilization, reuse for the development of construction and building materials, anaerobic bioenergy recovery, as well as sanitary landfill and odor control. Apart from the contribution to the promotion of fundamental science, the proposed technologies in our scientific work are of great promise in practice as well. Some of the technologies have been demonstrated by the great success of their full-scale implementations in the real-world scenarios, which made great contribution to sustainable sludge management in many cities in China. The positive outcomes encourage us to introduce our currently available scientific advances and well-proven experience to the world, especially to the countries that are the lack of proper sludge management strategies, and well-trained professionals.

This book covers contents of sewage sludge generation and characteristics, chemical and physical conditioning and deep dewatering, sludge solidification/stabilization, drying and incineration, sewage sludge-derived controlled low-strength materials, harvest of bioenergy by anaerobic digestion, and pollution control and recycling of sewage sludge in sanitary landfill. It will therefore provide environmentally friendly alternatives as well as valuable guidelines for engineers and researchers to address the sludge issues faced. In addition, it is convinced that the book also has the great potential to enhance promote the international exchange and cooperation of environmental researchers worldwide.

Summary

Continuous sewage sludge production is becoming one of the crucial issues in the field of water industries. In practice, the majority of sewage sludge has been sent directly to landfill sites without proper pretreatment while this practice is not environmental friendly. In this book, several environmentally friendly technologies for sewage sludge treatment and disposal have been introduced, including sewage sludge generation and characteristics, chemical and physical conditioning and deep dewatering, sludge solidification/stabilization, drying and incineration, sewage sludge–derived controlled low-strength materials, harvest of bioenergy by anaerobic digestion, and pollution control and recycling of sewage sludge in sanitary landfill, with the purpose of providing proper alternatives and valuable guidelines for engineers and researchers to address the sludge issues faced.

Abbreviations

AS   Calcined aluminum salts

ANC   Acid neutralization capacity

AVS-S   Acid-volatile sulfide

AD   Anaerobic digestion

AR   Aged refuse

CST   Capillary suction time

CSA   Calcium sulfoaluminate cement

CLSM   Controlled low-strength materials

CRS-S   Cr(II)-reducible sulfide

DS   Dewatered sludge

3D-EEM   Three-dimensional excitation-emission matrix fluorescence spectroscopy

DDSCOD   Disintegration degree

EPS   Extracellular polymeric substance

ES-S   Elemental sulfur

FT-IR   Fourier transforms infrared spectra

FA   Fulvic acid

FH   Ferric hydroxide

HA   Humic acid

LB-EPS   Loosely bound EPS

MSWI BA   Municipal solid waste incineration bottom ash

MOC   Magnesium oxychlorides cement

PS   Polysaccharides

PN   Proteins

PC   Portland cement

SCOD   Soluble chemical oxygen demand

S-EPS   Soluble/slime EPS

S/S   Solidification/stabilization

SEM-EDX   Scanning electron microscopy combined with an energy-dispersive X-ray spectroscopy

SV   Sludge volume

TSS   Total suspended solids

TCOD   Total chemical oxygen demand

TB-EPS   Tightly bound EPS

TG-DSC   Thermogravimetry-differential scanning calorimetry

TOC   Total organic carbon

TCLP   Toxicity characteristic leaching procedure

UCS   Unconfined compressive strength

VSS   Volatile suspended solids

WWTP   Wastewater treatment plant

WAS   Waste activated sludge

XRD   X-ray powder diffraction

ZVSI   Zero valent scrap iron

ZVI   Zero valent iron

Chapter One

Sewage Sludge Generation and Characteristics

Abstract

Sewage sludge, one of the main by-products from wastewater biological treatment process, is being continuously generated. It contains a myriad of toxic substances including pathogens such as viruses and worm eggs, heavy metals, and some organic contaminants, which create odors and hygiene concerns. Improper disposal and reuse of sewage sludge causes severe environmental impacts and health hazard to the public. The water industry is facing unprecedented economic and environmental constraints because of not only large amounts of sewage sludge produced but more stringent regulations. The processing of sewage sludge is one of the expensive items in a wastewater treatment plant, usually accounting for up to 50% of the total operating costs of the plant. Thus, the promotion of economically feasible treatment methods represents one of the most critical missions for environmental researchers. Nowadays, there have been several representative techniques for sewage sludge disposal applied in practice, for example, dewatering, composting, drying and incineration, anaerobic digestion, sanitary landfill, land application, and recycling as building materials. The technical feasibility of one method is dependent upon not only the degree of sludge stabilization, but also energetic and environmental benefits. In this chapter, sewage sludge production, special features of sewage sludge, and general processes of pollution control and resource recovery for sewage sludge are introduced; a deep comparison among dewatering, drying, incineration, composting, and sanitary landfill is made.

Keywords

Anaerobic digestion; Generation and characteristics; Incineration; Sanitary landfill; Sludge; Treatment of sludge

1.1. Sewage Sludge Production

In biological wastewater treatment process, the part of chemical oxygen demands (CODs) removed is converted into biosolids, which makes up sewage sludge. Sewage sludge usually represents 1–2% of the treated wastewater volume (Fig. 1.1). As per UN-Habitat's statistics, the existing wastewater treatment plants (WWTPs) in the United States, for instance, generate over 6.5  million tons of dry solids annually; it is estimated to be around 3.0 and 2.0  Mt per year produced in China and Japan, respectively (Fig. 1.2). The figures are naturally anticipated to increase in the near future when considering the growing applications of WWTPs in developing countries. The main disposal routes and rates are different in different countries, heavily depending upon the economic development level. As illustrated in Fig. 1.2, in developed countries such as the United States, the reuse and disposal rate reaches up to 94%, and it is roughly 97% in Japan, where more than half (52%) of sewage sludge is being recycled to produce building materials and 12% anaerobically digested for bioenergy recovery. Comparatively, the situation of sewage sludge use and disposal in developing countries is far beyond optimism. Note that for a sanitary landfill, the threshold of sludge water content is 60% from the view of safety regulations. The improper disposal not only causes the wasting of resources but also brings about a series of secondary disasters (e.g., landslide, environmental pollution, etc.). Sewage sludge management is highly complex and costly, representing a stern global challenge.

Figure 1.1  Sources and types of sewage sludge generated in wastewater treatment plants (WWTPs).

Figure 1.2  Estimated sewage sludge production as per the statistics of UN-Habitat and the situation of sewage sludge use and disposal. United States: From US Wastewater Treatment Fact sheet Pub. No. CSS04-14, 2015. China, Japan: Ministry of Land, Infrastructure, Transport and Tourism, Japan.

1.2. Special Features of Sewage Sludge

Sewage sludge floc is a multiphase medium and constitutes the vast majority of components including microbial aggregates, filamentous bacterial strains, organic and inorganic particles, extracellular polymeric substances (EPSs), and large amount of water. The composition of sewage sludge varies, depending upon the type and original components of the raw wastewater. EPSs, originating from the microbial activity (secretion and cell lysis) and/or from the wastewater itself, that is, from the adsorption of organic matter (e.g., cellulose, humic acids, etc.), are the major constituent of sludge organic fractions, mainly composed of proteins, polysaccharides, nucleic acids, humic substances, lipids, etc. (Fig. 1.3A). Depending on the spatial distribution within sludge floc matrixes, EPSs are usually divided into three categories: slime EPS (S-EPS), loosely bound EPS (LB-EPS), and tightly bound EPS (TB-EPS). S-EPS are evenly distributed in the aqueous phase and LB-EPS extend from TB-EPS and are characterized by a highly porous and dispersible structure; comparatively, TB-EPS adhere to the surface of the bacterial cells inside the sludge flocs (Fig. 1.3B). The presence of these three-dimensional, gel-like, and negatively charged biopolymers governs the surface physicochemical properties of sludge matrixes. EPSs provide the protective shielding and prevent the cell rupture and lysis, thereby influencing sludge functional integrity, strength, flocculation, dewaterability, and even biodegradability. Besides the protection from EPS, microbial cells themselves possess a hard cell envelope composed of glycan strands cross-linked by peptide that presents physical and chemical barriers to direct anaerobic digestion. In consequence, the sewage sludge with high EPS and cells-content has the stiff structure and will be more difficult to hydrolyze and digest.

Figure 1.3  Schematic representation of (A) the sewage sludge floc and (B) the sketch of extracellular polymeric substance (EPS) structure. (A) Modified from Urbain, V., Block, J.C., Manem, J., 1992. Bioflocculation in activated-sludge, an analytic approach. Water Sci. Technol. 25, 441–443.

1.3. General Processes of Pollution Control and Resource Recovery for Sewage Sludge

The term sludge treatment encompasses all alternatives that facilitate transport, storage, reuse, or final disposal of sewage sludge. The measures to avoid discharge into the environment need to be adopted compulsorily to protect human and environmental health from the risks linked to sludge (Fig. 1.4). The methods used most frequently for sludge handling and disposal include dewatering, composting, anaerobic digestion, drying–incineration, and sanitary landfill. An overview of various alternatives for treatment and disposal is presented in Figs. 1.5 and 1.6.

The main purpose of sludge dewatering is to reduce sludge volume by removing as much water as possible from the sludge. The water in sludge flocs is generally classified into four categories (Fig. 1.7): free water (65–85% of the total water), interstitial water (15–25%), vicinal water (7%), and water of hydration (3%). Free water is removed by gravity or flotation thickening. The removal of interstitial and vicinal water requires the addition of flocculants or strong mechanical forces. Water of hydration, retained in sludge flocs, can only be removed after harsh pretreatment such as thermal drying or freezing–thawing processes.

The composting is a biothermal aerobic process that decomposes the organic portion of sewage sludge and degrades the organic material by approximately 25%. Meanwhile, the heat can be generated during this process, which reduces the moisture content of the sludge. The process performance strictly relies upon temperature, dry matter, and volatile solids (VS). In general, the sludge used for composting should meet the requirements of below 60% moisture, over 40% organic matters (dry basis), and acceptable level of heavy metals and POPs as regulated. When the 80% moisture sludge is used for composting, lower moisture organic matters, such as straw, sawdust, should be added to adjust the water contents to around 55–65%. Moreover, strong odor will generate during composting process, which is very difficult to effectively control.

Figure 1.4  Illegal sewage sludge discharge directly into the environment.

Figure 1.5  Treatment and disposal routes of sewage sludge.

Figure 1.6  Treatment and disposal of sewage sludge and corresponding environmental impacts.

Figure 1.7  Water distribution of sewage sludge.

Anaerobic digestion comprises several successive biological processes (i.e., hydrolysis, acidogenesis, acetogenesis, and methanogenesis) in which microorganisms break up biodegradable matter and produce methane-rich biogas (60–70  vol% CH4); it also reduces the amount of final residual solids for disposal while destroying the pathogens present in the sludge and eliminating offensive odors. The digested residual is disposed of in agriculture fields as soil conditioner/fertilizer, when it meets the environmental constraints reflected by the local regulations and standards. Anaerobic digestion is thus regarded as a major and essential part of a modern WWTP. In some cases, the heavy metals in the residues may be too high to be used in agriculture and should be landfilled. To date, three types of anaerobic processes (or digesters) have been proposed and commercially applied in the real world (Fig. 1.8), such as single-stage process in which the bioconversion of sludge is completed in a single chamber, double-stage process where the acidogenic and methanogenic stages are separated into two chambers, and temperature-phased anaerobic digestion (TPAD) that combines a thermophilic pretreatment unit prior to mesophilic anaerobic digestion.

Figure 1.8  Schematic diagrams of single-stage process, double-stage process, and temperature-phased anaerobic digesters (TPAD).

The obstacles for anaerobic digestion of sludge include the relatively lower organic matters and high inorganic matters. Silt, sand, gravel, and wood may be present in the sludge, which makes the digestion very difficult and low output of biogas, resulting in a high operation cost and low weight reduction. The residue generated in the digestion has no way to go as it still contains biodegradable matters and should be composted before using in agriculture and city green plantation. Sanitary landfill seems to be the ultimate way for these residues.

Drying and incineration can totally carbonize organic constituents in sludge and minimize the volume of sludge (90% reduction). The chemical energy in the dried sludge can be harvested during combustion and subsequently employed for thermal drying. Nonetheless, thermal drying is not a cheap option because of its high energy demand to remove biologically bound water from sludge. The economics of the process depend upon dry matter content, VS/TS (total solids) ratio, and calorific value (Fig. 1.9). Meanwhile, the resulting combustion ash can be used as a raw material for the manufacture of different building materials such as sintered bricks, tiles, pavers, or Portland cement if it is justified as a general waste other than a hazardous waste.

Fig. 1.10 shows the typical schematic diagram of a typical sludge drying and incineration process. In the conventional drying and incineration process, the drying and incineration operations are separated. The sludge is first dried in one equipment and then incinerated in another incinerator. The heat for sludge drying may be from burning of oil, natural gas, coal, and even electricity. The heat from the dry sludge is also used for the sludge drying. To raise the heat utilization efficiency, some equipment makes the hot flue gas from coal combustion direct contact with sludge. In this case, the oxygen content in the drying system must be controlled very carefully, otherwise explosion may occur. Indirect drying process will lead to a lower heat utilization efficiency and thus will raise the cost.

Figure 1.9  Sludge calorific value versus water content (or dry solids content).

Figure 1.10  Flow sheet of a typical sludge drying and incineration process.

1.4. Sanitary Landfill of Sludge

Sanitary landfill has been viewed as an ultimate disposal site for sludge. One of the critical factors affecting sludge landfill is its rheological properties. Dewatered sludge with around 80% moisture and a low compressive strength makes the landfill operation impossible because of construction difficulties and instability of the landfill slopes. According to the practical experiences gained in the real landfill for sludge landfill, the moisture of sludge should be below 60% when being disposed of in a landfill to support the weight of operation equipment and to prevent the deposited sludge from the sliding disaster. Therefore, different solidifying additives, including aged refuse, magnesium salts, coal ash, demolition wastes, lime, and soil, have been adopted to modify sewage sludge so as to transform the geotechnical properties. Taking Shanghai Refuse Landfill, the biggest landfill in China, as an example, all of sewage sludge has been landfilled after modified with aged refuse and magnesium salts, conducted by the authors (Fig. 1.11). According to the authors' research and experiences, the common modification methods and mixing ratios are provided in Table 1.1, which can be referred as references for sewage sludge sanitary landfill.

Sludge could meet the requirement of shear stress and bearing capacity of not less than 50 and 25  kPa, respectively when its moisture content decreased to 64%. Side slope of 12.6  degrees may be constructed without causing sliding problems during landfill operation. The malodor could decrease to third grade. Consolidation coefficient under 50  kPa was calculated to be 0.010726  cm²/s, and the compressive coefficient under 50–100  kPa was 1.16.

Figure 1.11  Flow sheet of a typical sludge solidification and sanitary landfill process.

Table 1.1

Common Modifying Additives and Mixing Ratios of Sewage Sludge

It was found that the geotechnical properties of sludge for landfill operation should meet the requirements of the following specifications: bearing capacity over 50  kPa, vane shear strength over 25  kPa, permeability of over the magnitude of 10−⁶∼10−⁵  cm/s, and moderate odor. In this case, the sludge should be mixed with the additives, and the ratios of additives to sludge should be over 6:10, 9:10, 7:10, and 9:10 for coal fly ash, aged refuse, demolition wastes, and soil, respectively.

The annual production rate of leachate from fresh sludge with a moisture of 80% was about 44  L/t. The biodegradability of leachate decreased and annual production of leachate increased to 287  L/t in the presence of 33% aged refuse in the mixtures. Meanwhile, it was observed that the presence of the additives can accelerate the stabilization of sludge. Pollutants' concentrations in leachate from mixtures with additives were always lower than those of the fresh sludge.

A field lysimeter with 36  t of fresh sludge was established and its long-term stabilization process was monitored. It was found that pollutants’ concentrations in the leachate from the field-test lysimeter were significantly lower than those of the laboratory lysimeters. Moreover, it seemed that the degradation in the field lysimeter was faster. After 498  days' biodegradation, the organic matters decreased by 67.1%, 61.6%, 30.5%, and 51.4% for the laboratory-scale lysimeters of biosludge, biosludge  +  aged refuse, chemical sludge, and field-test lysimeter of chemical sludge, respectively. The biodegradation of the biosludge was observed to be faster than the chemical sludge. It was found that humus, humic percentum, and humic index slightly increased during the stabilization process. Molecular weight of humic acid decreased in early days revealing its mineralization process and increased with time in metaphase and anaphase showing its maturation process. Fulvic acid decomposed in prophase and composed in metaphase and anaphase. Humic percentum decreased in the sequence of the laboratory-scale lysimeters of biosludge  +  aged refuse, biosludge, field-test lysimeter of chemical sludge, and chemical sludge, whereas humic index decreased in the sequence of the laboratory-scale lysimeters of biosludge, biosludge  +  aged refuse, field-test lysimeter of chemical sludge, and biosludge.

Biological toxicity faded during the stabilization of sludge, slow in prophase and rapid in metaphase and anaphase, according to the logarithm formula. The germinating index of biosuldge, aged refuse  +  biosludge, chemical sludge and field-test chemical sludge can reach upto 80% at 612, 626, 650, and 670  days of placement, respectively. Mixing of aged refuse could reduce the toxicity of the biosludge and increase the germinating index.

Settlement of simulated landfills could be classified into the initial stress settlement occuring mainly in the first year and secondary degradation settlement in the following years. The predicted ultimate settlement of the chemical sludge in field-test lysimeter, chemical sludge, biosludge, and aged refuse  +  biosludge in the laboratory-scale lysimeters were evaluated to be 12.33%, 20.54%, 13.77%, and 26.57% of the initial sludge height, and the corresponding settlements in first year were 98.9%, 94.4%, 97.4%, and 98.9% of the ultimate settlement, respectively. 99.99% of the ultimate settlement may reach at 870, 1170, 995, and 762  days of the placement, respectively. Consolidation coefficient of field-test lysimeter was calculated to be 0.00249  cm²/s.

The equations among the settlements, pollutants' concentrations in leachate (COD, NH3-N, etc.), chemical compositions in the sludge (organic matters, BDM, VS, TS, moisture, etc.), and the placement time were established. Taking the leachate discharge standard and the BDM in soil as reference, it was estimated that the resultant biodegraded sludge can be regarded as the stabilized sludge or aged sludge that can be excavated and recycled after around 5.82-year placement, when the BDM in the sludge decreased from around 30–60% in sludge to 4.76% in soil and COD to 100  mg/L in the leachate. If the aged sludge was to be used for planting, 1.68–1.84  years at least would be needed.

Chapter Two

Enhanced Sewage Sludge Dewaterability by Chemical Conditioning

Abstract

oxidation with mild-temperature process or electrolysis are also conducted to maximize the